1. Field of the Invention
The present invention relates to a multiple data management method carried out in a system in which a host computer and primary and secondary storage devices are connected as capable of communicating with each other via a network, the primary and secondary storage devices functioning as a data storage device of the host computer. Particularly, the present invention relates to a multiple data management method utilizing the Internet as the network.
2. Description of the Related Art
For example, in Japanese Patent Application Laid-open Publication No. Heil0-333838, a multiple data storage system is disclosed, in which data of a first storage subsystem is managed in parallel also in a second storage subsystem connected thereto via a dedicated line or the like for the purpose of securing data integrity and the like in the event such as a disaster. Moreover, in the publication, a synchronous method and an a synchronous method are disclosed as operational methods for the multiplexing storage system. Specifically, the synchronous method is one for maintaining synchronism of primary and secondary storage devices. The a synchronous method is for reducing a waiting time of a host computer in such a manner that, regardless of whether or not writing of data at the secondary storage device is completed, a completion report is immediately transmitted to the host computer when writing of data at the primary storage device is completed.
Moreover, for example, in Japanese Patent Application Laid-open Publication No. Hei9-325917, disclosed is a technology utilized in an operation by the asynchronous method among the operational methods disclosed in the above-described publication. Specifically, by use of the technology, in the case where a primary storage device is down because of a disaster and the like during the time when update states of the primary storage device and an secondary storage device are inconsistent with each other, the secondary storage device grasps the presence/absence of erased data at the secondary storage device side and the data is restored.
Incidentally, as to a technology of multiple data management of a primary storage device by a remote secondary storage device, various technologies have hitherto existed such as the one described above. Recently, with the spread of the Internet, an environment in which the Internet can be utilized easily and inexpensively at various locations has been completed. Thus, it is anticipated that, in the years ahead, there will be increasing cases of utilizing the Internet as a network connecting the primary and secondary storage devices, a computer using those devices and the like. Moreover, it is also anticipated that, from now on, there will be more cases of multiple data management in a personal computer and the like by use of remote storage devices connected via the Internet.
However, the Internet has characteristics different from those of a dedicated line and the like in view of its nature of having its midway routes operated by the general public (for more detail as to such characteristics of the Internet, refer to RFC 791 “INTERNET PROTOCOL,” for example). In order to construct a multiple data management system utilizing the Internet as communication means, a mechanism that takes into account such characteristics of the Internet is necessary.